Degreasing metal strip



Patented July 2i,v i942 UNITED STATI:

PAT

*nn'GasAsmGMErAL sV William Edward Booth, Buncorn, England, as'- signorto Imperial Chemical Industries Limited, a corporation of Great Britain'v v Application retruary 12, 1940, serial No. 318,666

In Great Britain February 20, 1939 12 claims. (ci. goa-170) 'Thisinvention relates to degreasing metal strip bytreating it with avolatile solvent.

It has previously been proposed to degrease metal strip by treating it;with the vapour of a volatile solvent. In order that solvent lossesduring such aprocess may be minimized it is essential that the stripshall be dry when leaving the apparatus.v When degreasing metal castingsand similar heavy articles, they are usually-'dried by keeping them,while still hot. in the solvent 'f f vapour for a short time.

This methodis not eiective for metal strip because .of'its low heatcapa'city per unit length, and, indeed, drying metal strip which hasbeen degreased in solvent vapour is a problem peculiar to that material,

xed ysmooth rods areidisposedat or near, the point where the stripleaves -thevapour zone,

4 so that each surface of the strip contacts atleast one 'roller or rodin passing to the exittube.,

In addition to the solvent vapour zona-*fone or more liquor treatmentcompartments, or a spray treatment compartment may also be provided.

particularly when the degreasing'process is a* continuous one. getherwith the above mentioned requirement of These drying dimcuities', to-

minimizing solvent losses, have hitherto set a l limit to the speedat'which themetalstrip can be passed through such a solvent degreasingap'- j One'method for treating metal strip with volatile solvent hasbeen described, in which the strip is withdrawn through an almosthorizontal" tunnel-like enclosure abovethel vapour level and having acondensing coil adjacent to its lower surface. Such a device has thedisadvantage of increasing the overall length ofthe plant, and

.is not entirely satisfactory since solvent laden air tends tov escapeat the exit of the tunnel,

and this tendency can only be counteracted bv running the metal stripthrough the plant at low speeds.

The apparatus oi the present invention, on

Y the other hand, is capable of operation at much greater` speeds thanhave hitherto been feasible.

while entailing smaller Vsolvent losses; According to the presentinvention, therefore, an apparatus for the continuous degreasing oil,metal strip by treatin'gvit with a volatile grease a'solvent whose`vapour is'heavier than air, com-` prises a closed vessel having anentrance and exit for the metalstrip, means for maintaining 'a solventvapour zone within the said vessel, means 'being providedV to causethevl into and thr`ough the degreasingzonaf A winding mechanism may beprovided beyond ythe exit placedbei'ore the vapour compartmentin thepath of the strip.

I'he entrance for the. metal strip may bemerely a slit in the casingabove the solvent vapour level, as determined,.for example, by coolingcoils around the sides of the vessel, rollersor guides side .of thelapparatus to roll .up tne degreased strip and'puli it through theapparatus.` Alternatively, the stripmay. pass between a pair :of

rollers at or beyond the'end of the exit tube which grip the strip'andwhich are driven by suitable ,means so asto pullthe strip outv of the'appa-A ratusY as they frotate. We iind it preferable, however, toprovide at the entrance a device sim- --rilar to that which we provideat-the exit. that visto say, a tubeiitt'ed with cooling me'ansandextending upwards from the Y degreasing vessel,

preferably to approximatelythe same height as the tube at the exit.Alternatively, the strip may be introduced and removed throughfthefsamecause the strip to pass f it is advantageous 'to :give the ks'trjip 'arinse 'with pure solvent shortly'beiore'its removal from f forintroducing metal strip intosaid vessel, a

tube.

Preferably` the exit is above the vapour zone l and the tube extendsinto the plant below the shaped vessel having" `and feeding to the tube,suitable rollers or guides being provided to areA included. In anyapparatus comprises a vapour compartmentonly'.

the vapour zoneinforder to removeadherent 4insoluble solids; where;fasisy almost yinvariably the case, condensing C Qils around the insidewalls 1 of the vesselare used j i o limit upwardly'the vavpcnir-zone,this 'may bedoneby providing below the level of the coils 'andpreferably near the exit for the metal strip,` a horizontal trough-L atits lowest .part a slit passes in an upward direction, trough puresolvent, e.r g.' vconthrough the strip densate from thecondensing,coils. f Both sides loi' the strip are thus stapte pass down'A through the vapour zone and the liquor or spray compartments wheresuch our invention the tubes may be pivtedat the base to facilitatethreading the stripthrouglithel apparatus- I f:

In some cases, particularly" when thedegreasing l mashedv Wahine ,streamor, f l vapour leven-preferably also, staggered rollers or 55 solventwhich will'iiow through the slit counter.

extending above the vessel.

- 'pulling it over the rollers. *i l In using this apparatus the stripis threaded through the apparatus,` passing zig zagbetween the rods atthe base of the exit tube, so that both cooling water are turned on tocooling coils and -illm is rapidly evaporated,to be recondensed on 2current to it, and insoluble matter will be washed i olf.

In one form of our invention the apparatus comprises -a closed vessel,vaporising means, e. g. a sump fitted with heating coils, formaintaining ,a solvent vapour atmosphere in the vessel and coolingkcoilsin the upper part to condense vapour and returnv it to the sump orother vathe vapour` level to admit metal strip.. and at the other end avertical water-iacketed tube The inner walls of the tube are continuedbelowthe top of the vessel to just below the level of the cooling coils,and are expanded into a small chamber between the 'cooling coils and thetop of the vessel to contain three horizontal parallel nxed rods oneabove other, the middle lone being displaced in a vertical planerelative to the other two. Rollers are also provided at the upper end ofthe vertical exit tube and within thedegreaser to guide the stripthrough the vapour zone. A winding mechanism beyond the apparatus windsup the degreased strip and serves asa means for surfaces make contactwith a rod. Supplies of water jacket, and vapour is generated. As thestrip is passed through the apparatus the vapour condenses on it, andthe condensate dissolves the grease; the majority ofthe solvent thenfalls porizer. The vessel has a slit at one end above lengths of thetubes. Tubes l and 8 are pivoted at il to facilitate the threading ofthe strip Il. In their normal position the tubes form a vapourtight sealat the Junction with vessel I. By means of nanged pulleys Ii the stripcan be fed down through tube I into the vapour zone and out againthrough exit tubel after ypassage through the vapour zone. Tube 8 has anextension Il reaching downwards to the level of the bottom of thecondensing coils,` and within extension Il are three horizontalstaggered rollersv I2 one above the other.; Immediately below theextension I Iis a V-shaped trough i3 having a slit I4 at the angleotf'the V to which condensate from trough l'can be fed via plate Il servingboth as .a support i'or trough I3 and a surface over which solvent canfiow'to it. A winding apparatus (not Il to the winding apparatuswhichpulls thev strip through the degreasing apparatuswhen the lil within thedegreasing compartment, threaded Y through slit Il in trough I3, betweenrollers l2 so that both vsurfaces contact the rollers, up through tube.C and over the remaining pulley j latter'is inoperation., The "supplyof cooling liqback into the sump. As the strip rubs against ljtherollers most of the condensate stilladhering is removed, leaving buta thiniilm to be carried into the jacketed tube.f The strip being stillpractically at thev temperature of the vapour ythis the cold waterjacket and fall back into the .vapour zone. The vertical position ofthetube ensures that heavy solvent-laden air will not i remain inthe tubeand interfere with the further evaporation of `solvent adhering tothestrip, while because the solvent vapour is so much denser than air thecontinuation ofthe jacket into the,

vapour zone creates a seal which prevents through draughts of air beingset up which would entrain solvent vapour and carry it out of theapparatus.. .l i i A further form of our invention, including a In thisdrawing the closed vessel l has a sump z in itsjiower part provided withesteem con s by which solvent can be vaporized; around the inside wallsof the upper part of the vessel are condensing coils 4 which can beprovided with a cooling liquid by mean's notA shown.VImmediately'beneath coils l is atrough B to collect condensate from thecoils. From 'one' end of the `vessel i a. iacketed tubel B extendsvertically upf 4, carriedA outmore rapidlythan has hitherto been wardsand has aninlet and outlet 1, lby which cooling liquid, e. g.`,`water orbrine, can becirculated through the jacket. At the other end ofthevessel is a second similar jacketed tubel 8 having aninlet and outletl, v9, by which cooling liquid can be suppliedto thezjacket; the tubeextends vertically upwards to substantially the same height as the firsttube. As` shown on the drawing the cross-sectionalareas of tubes l and 8are relatively restricted vas compared to the uid to the Jackets oftubes and l and tocoils 4 is then commenced and the solvent vapour zonesetup by-boiling solvent yin sump 12 bycoil I. Degreasing then proceedsas the strip is pulled through, the main degreasing proceeding as the.strip passes between'the'pulleysvv I0 within the vapour zone, but asupplementary washing of the hot stripbeing applied as it passes throughslit' Il countercurrent to fresh condensate nowing from trough loversurface I5 into trough Il and thence downv through .slit I4 to fall intosump 2. As thestrippasses over rollersli adherent solventis removed,leaving atl most a thin nlm on the stripas it enters the tube 8. Sincethe strip will stillbe substantially at the temperature of the vapourthis iilm ywill evaporate rapidly and be recondensed on the cold waterjacket to fallback into the ,vapoury zone. .The vertical position of the.tube and the action of the cold water jacket ensure that rheavy solventvapourladen air will not remain in the tube and im-v pede theevaporation of solvent adhering to the strip; thus the .whole dryingprocess is accelerated, and since it is this which in practice sets `alimit to the speedat-which degreasing can be carried out, the operationas a whole zcan be possible. 1

' Since extension AI I of .tube l extends below. the solvent vapourlevel a seal is formed by the heavy solvent vapour, and through draughtsof air cannot be set up entraining vapour 'and carrying it out of theapparatus; this possibility is still further diminished by the-:lacketedtube vi at the entrance, since any solvent tending .todin'use'up into thistubewill be'condensed on the Jacket;

moreover as the tubes I and ,l are the same height, balanced columns o'fair inthe two tubes are created which-balance saam diminishes mytendency for currents of'air to circulate through the apparatus.

Iclaim: 1` 1. Apparatus for fthe continuous degreasing of metal strip bytreatment with a volatile .grease solvent the vapour of which is heavierthan air;

comprising a closed vessel having an entrance and an exit for the metalstrip, means for maintaining a solvent vapour zone within the s aidvessel, means for introducing metal strip into thel vessel, a tube atthe exit provided with cooling means and extendingsubstantially-vertically upwards from the said vessel. said coolingmeans comprising a water jacket surrounding said tube above the level ofsaid vessel, and means for withdrawing the treated metal strip from thevapour zone through the said tube.

2. Apparatus according to claim l in which the tube through which themetal strip is withdrawn extends downwards into the vessel to a pointbelow the solvent vapour level.

3. Apparatus according to claim l in which staggered guides are disposedat or near the point where the striplleaves the vapour zone so that eachsurface of the strip makes contact with at least one such guide inpassing to the exit tube.

4. Apparatus for the continuous degreasing of metal strip by treatmentwith a volatile grease solvent the vapor of which is heavier than air,said apparatus comprising a closed vessel hav- .ing an entrance and anexit for the metal strip;

means for maintaining a solvent vapor zone within said vessel; means forintroducing metal strip into said vessel; a tube positioned at the exit,said tube extending substantially vertically upward from said vessel andbeing provided with cooling means consisting of a water jacketsurrounding said tube above the level of said vessel; means forwithdrawing the treated metal strip from the vapor zone through saidtube; a liquid solvent receptacle positioned within said vapor zone,said receptacle being provided at its bottom with an opening for passingthe metal strip upwardly therethrough and for simultaneously drainingsolvent downwardly therethrough, whereby to effect countercurrentwashing of said strip with said solvent; and means for deliveringv puresolvent to said receptacle.

5. Apparatus for the continuous degreasing of metal strip by treatmentwith a volatile grease solvent the vapour of which is heavier than air,comprising a closed vessel with means for maintaining a solvent'vapourzone therein, an entrance tube extending substantially verticallyupwards from the said vessel provided with cooling means and with meansfor introducing metal strip into the vessel through the said entrancetube, and an exit tube similarly extending substantially verticallyupwards from the vessel provided with cooling means and with means forwithdrawing the metal strip from the vapour zone through the said exittube, both of .said cooling means comprising water jackets surroundingthe respective tubes above the level of said vessel.

6. Apparatus according to claim in which at least one of theupwardly-extending tubes extends downwards into the vessel to a pointbelow the solvent vapour level.

7. Apparatus according to claim 5 in which staggered guides are disposedat or near the point where the strip leaves the vapour zone so that eachsurface of the strip makes contact with at least one such guide inpassing to the exit tube.

8. Apparatus for the continuous degreasing of therein; an entrance tubeextending substantially vertically upwards from said vessel and providedwith cooling means consisting of a waterv jacket surrounding said tubeabove the level of said vessel and with means for introducing metalstrip into the vessel through the said entrance tube; an exit tubesimilarlyextending substantially vertically upwards from the vessel andprovided with cooling means consisting of a water Jacket surroundingsaid tube above the level of said vessel and with means for withdrawingthe metal strip from the vapor zone through the said exit tube; a liquidsolvent receptacle positioned within said vapor zone, said receptaclebeing provided at its bottom with an opening for passing the metal stripupwardly therethrough and for simultaneously draining solvent downwardlytherethrough, whereby to effect countercurrent washing of said stripwith said solvent; and means for delivering pure solvent to saidreceptacle.

9. Apparatus for the continuous degreasing of metal strip by treatmentwth a volatile grease solvent the vapour of which is heavier than air,comprising a closed vessel with means for maintaining a solvent vapourzone therein, a tube extending substantially vertically upwards from thesaid vessel provided with cooling means and with means for introducingmetal strip into the vessel through the said tube and for withdrawingthe strip after treatment through the same tube, said cooling meanscomprising a water iacket surrounding said tube above the level of saidvessel.

10. Apparatus according to claim 9 in which the upwardly-extending tubeextends downwards into the vessel to a point below the solvent vapourlevel.

1l. Apparatus according to claim 9 in which staggered guides aredisposed at or near the point where the strip leaves the vapour zone sothat each surface of the strip makes contact with at least one suchguide in passing out of the vessel into the upwardly-extending tube.

l2. Apparatus for the continuous degreasing of metal strip by treatmentwith a volatile grease solvent. the vapor of which is heavier than air,said apparatus comprising a closed vessel with means for .maintaining asolvent vapor zone therein; a tube extending substantially verticallyupwards from the said vessel; cooling means for said tube consisting ofa water jacket surrounding said tube above the level of said vessel;means for introducing metal strip into the vessel through the said tubeand for withdrawing the' WILLIAM EDWARD BOOTH.

